Suspicious Operation

Maybe I’m being silly here, but everytime I boot up my AVAST 4 Home edition (eventually) pops up a window (a white one similar to old 3.1 windows) stating “Standard Shield has detected a suspicious operation” and names a dll file from the AVAST directory (i can’t remember which). I get to choose YES, NO, or IGNORE, but it doesn’t say what each of these options does, i’ve tried them all by rebooting several times to see and nothing different happens.

Occassionally I get the same message but for a different dll file, for example when I run other programs (such as Corel DRAW 9). Is this the sign of a virus? I ran a complete Thorough Virus Scan of my entire system but it found nothing.

Any ideas?

Thanks in advance,
Richard.